Step & repeat type or step & scan type exposure apparatuses play a dominant role in the semiconductor integrated circuit manufacturing process. Such an exposure apparatus exposes the surface of a substrate (to be referred to as a wafer hereinafter) coated with a resist to the circuit pattern of a mask or reticle (to be referred to as a reticle hereinafter) via a projection lens. Recently, the integration degree of semiconductor integrated circuits is increasing. Along with this, demands have arisen for a light source for emitting exposure light having a shorter wavelength. In particular, a rare gas hydride excimer laser (to be referred to as an excimer laser hereinafter) as a kind of laser oscillation apparatus is receiving a great deal of attention as an ultraviolet high-output laser.
An exposure apparatus is generally used in a clean room. As the atmospheric pressure in the clean room changes upon changes in weather, the refractive index of exposure light changes, and the imaging position of a circuit pattern varies. In general, an excimer laser for the exposure apparatus can change the oscillation wavelength within the range of about 300 to 400 pm. The refractive index of exposure light changes depending on the wavelength. For this reason, the atmospheric pressure in the use environment of the exposure apparatus is measured at a proper timing such as the start of a job or exchange of a wafer, an optimal oscillation wavelength which should be oscillated to cancel variations in imaging position caused by a change in atmospheric pressure is calculated, and the oscillation wavelength of the excimer laser is changed by a desired amount. In this manner, the exposure apparatus copes with a change in atmospheric pressure in the use environment of the exposure apparatus.
This exposure apparatus performs exposure by a processing flow as shown in FIG. 12.
After the start of a job (step 901), the atmospheric pressure near the projection lens is measured at a proper timing such as a wafer loading timing (step 902). The main controller of the exposure apparatus calculates an oscillation wavelength (target oscillation wavelength value) optimal for exposure on the basis of the atmospheric pressure (step 903). The target oscillation wavelength value is transmitted to an excimer laser controller (step 904). An excimer laser oscillation apparatus closes a shutter arranged at an excimer laser exit port (step 905). The excimer laser controller emits a test excimer beam while oscillating a pulse beam, and adjusts the oscillation wavelength within a predetermined allowable range by using a wavelength change means while monitoring the oscillation wavelength by using the internal optical measurement unit of the excimer laser oscillation apparatus (step 906).
The laser oscillation apparatus checks whether the oscillation wavelength falls within a predetermined allowable range of a predetermined target oscillation wavelength value (step 907). If NO in step 907, the excimer laser changes to an error state and stops oscillation (step 908). If YES in step 907, the laser oscillation apparatus transmits a wavelength lock signal “ON” representing this to the exposure apparatus, opens the shutter (step 909), and starts exposure in accordance with an emission signal from the exposure apparatus (step 910). After exposure, the wafer is unloaded (step 911), and whether to expose the next wafer is determined (step 912). If NO in step 912, the job ends (step 913); if YES, the flow returns to step 902.
In the prior art, every time the oscillation wavelength is changed, the shutter must be closed to emit a test laser beam in order to confirm whether the changed oscillation wavelength reaches a target value. Shutter opening/closing operation and test emission decrease the productivity of the exposure apparatus.